METHOD

Melt chocolate in a heatproof bowl over a saucepan of simmering water. Stir until smooth. Cool slightly.

Using an electric mixer, beat butter, peanut butter and sugar in a large bowl until pale and creamy. Add eggs, one at a time, beating until combined. Add flour and milk, in two batches, stirring until combined. Spoon half the cake batter into another bowl.

Stir cooled chocolate into one bowl. Drop spoonfuls of the two cake batters, alternately over the base of the pan. Using a knife to swirl mixtures to create a marbled effect. Bake for 1 hour- 1 hour 10 minutes, or until a skewer inserted into the centre comes out clean. Stand in pan 10 minutes. Turn out onto a wire rack to cool.

For icing, combine all ingredients in a heatproof bowl. Sit bowl over a saucepan of simmering water. Stir until melted and smooth. Cool slightly. Spread over cooled cake. Sprinkle with peanuts. Serve.